Method of producing steel wire and strand for pre-stressed concrete construction

ABSTRACT

A method of producing steel wires and strands for pre-stressed concrete construction, with low relaxation value and excellent straightness, which comprises applying in the ordinary lowtemperature annealing range of 300*-400*C to cold drawn steel wire and strand formed therefrom containing 0.6 - 0.9 percent of carbon, a tension corresponding to 10-50 percent of the tensile strength of the cold drawn wire at room temperature and, at the same time, a bending stress so as to give 0.1-0.5 percent maximum surface strain.

Elite States iatet Suzuki et al.

[ Nov. 12, 1974 METHOD OF PRODUCING STEEL WIRE AND STRAND FOR PRE-STRESSED CONCRETE CONSTRUCTION Inventors: Akira Suzuki, Chibashi; Masaki Hagiwara; Nobuhiro Teraoka, both of Tokyo, all of Japan Assignce: Suzuke Metal Industry Co., Ltd.,

Kitaku, Japan Filed: Dec. 29, 1972 Appl. No.: 319,712

Foreign Application Priority Data June 13, 1972 Japan 47-58177 148/12 Int. Cl B2lf 9/00 Field of Search 148/12, 130; 266/3; 140/2; 72/128, 378, 183, 364

[56] References Cited UNlTED STATES PATENTS 3,130,088 4/1964 Cook v. 148/12 3,469,829 9/1969 Fujita et all... 3,580,746 5/1971 Behar 3,605,469 9/1971 Queralto 148/12 Primary E.\'aminerLowcll A. Larson Attorney, Agent, or FirmWenderoth, Lind & Ponack ABSTRACT A method of producing steel wires and strands for prestressed concrete construction, with low relaxation value and excellent straightness, which comprises applying in the ordinary low-temperature annealing range of 300400C to cold drawn steel wire and strand formed therefrom containing 0.6 0.9 percent of carbon, a tension corresponding to 10-50 percent of the tensile strength of the cold drawn wire at room temperature and, at the same time, a bending stress so as to give 0.1-0.5 percent maximum surface strain.

7 Claims, 7 Drawing Figures PAIENTEDHUY 2 IIIII 3.8471102 SHEEI 2 or 3 A- HOT SIMPLE TENSION PROCESS A B- PRESENT INvENTIvE PROCESS MAXIMUM STRA|N= 0.4% [6 C-PRESENT INvENTIvE PROCESS MAXIMUM STRAIN o. 3%

RELAXATION vALUE (I00 HR) I I"I ov IO I v SPECIFIC LOAD TENSION /ACTUAL ULTIMATE T NSILE STRENGTH x IOO)% FIGS PAIENIEDIIIIV I 2 I974 3847l002 sum 3 r 3 A-I-IOT SIMPLE TENSI0N PR0cESS LU B-PRESENTINVENTIVE PROCESS g MAXIMUM STRAIN =02 2 I0 0- PRESENT INvENTIvE PROCESS L6 I MAXIMUM STRAIN=O.3-O.5%

LIJ K D I (I D SPECIFIC LOAD FIG.6

0 SPECIMEN TREATED BY ORDINARY PROCESS O 0 SPECIMEN TREATED BY PRESENT 1 lNvENTIvE PROCESS E I 2 i Z 9. if 4 X I v E 6 I I I I TIME RE UIRED FOR EXPERIMENTS (HOUR) FIG.1

METHOD OF PRODUCING STEEL WIRE AND STRAND FOR PRE-STRESSED CONCRETE CONSTRUCTION The present invention relates to a method of producing wire and wire strand for pre-stressed concrete construction.

conventionally, it is common practice to straighten cold drawn wire (in the case of wire strand, straightening is done after stranding) and to subject the wire to stress relieving (low temperature annealing) for production of wire for pre-stressed concrete construction. By this stress relieving, the wire is improved in yield strength, elongation and stress relaxation, which are important properties of wire used for pre-stressed concrete construction.

Recently, low relaxation pre-stressing wires have been increasingly in demand for large pre-stressed concrete constructions such as pre-stressed concrete pressure vessels, bridges and piles.

As a method for producing such low-relaxation wire for pre-stressed concrete construction, it has been proposed to heat cold drawn plain carbon steel wire containing 0.35 0.9 percent carbon while applying tension to the wire so as to give it permanent elongation of less than 5 percent. (US. Pat. No. 3,196,052). Another method has been proposed in which wire is advanced along a rotary member of progressively increasing diameter so that strain is applied gradually to the wire in the direction of the wire advancement, the wire also being heated to a certain temperature so as to give it a predetermined permanent elongation (US. Pat. No. 3,068,353).

By the above methods, it is possible to obtain lowrelaxation wire for pre-stressed concrete construction, but it is necessary to apply a substantially large load to obtain satisfactory straightness of the wire. The result is that very dangerous operations accompanied by possible rupture of the wire are often necessary and very close control is required for the wire pulling operation. The permanent elongation in connection with specially increased temperatures is determined by the diameter of some rotary members. There is a defect, however, in that the wire is subjected to repeated bending while it passes around the rotary member, and that the wire attains a maximum temperature just before the rotary member which applys the permanent elongation, due to the direct resistance heating system, so that the wire strength and yield point being prevented. (Japanese Patent Publication Sho 45-29096). With the above proposed method, however, the straightness of the steel wire is not satisfactory and almost no improvement of 5 the relaxation value can be expected.

One of the objects of the present invention is to provide an advantageous method for producing steel wire and wire strand for pre-stressed concrete construction which is free from the above defects and less susceptiand other mechanical properties.

Another object of the present invention is to provide a method which can produce steel wire and wire strand for pre-stressed concrete construction economically and by a simplified process.

Through extensive experiments for overcoming the defects of the conventional methods and for attaining the above-mentioned objects of the present invention, -the present inventors have found that when cold drawn steel wire or steel wire strand after working is subjected simultaneously to tension and bending stress within the ordinary stress relieving temperature range, similar or lower relaxation values, compared with those obtained by conventional methods, excellent straightness, and similar or higher tensile strength and yield strength, compared with those obtained by conventional methods, can be attained very easily and stably with less ten sion.

In short, the objects of the present invention can be attained by applying simultaneously tension and bending stress to cold drawn steel wire or steel wire strand after working in an ordinary stress relieving temperature range.

As above described, the present invention is characterized in that steel wire or steel wire strand is subjected simultaneously to tension and bending stress while it is kept hot, so that the high tensile strength, high ductility and low relaxation, as well as precise straightness, required for steel wire for pre-stressed concrete construction, can be obtained. By hot tension and bending, not only is the tension normally required for simple tension application for obtaining desired improvements is remarkably moderated, but also straighter wires are obtained. As compared with simple bending, remarkable improvements in material qualities are obtained.

Table 1 shows comparisons between various conventional processes and the present inventive process.

' TABLE 1 Ordinary Process Cold drawing-[m Straightening Low temperature annealing.

Hot Simple Tension Process Cold drawing[m Hot simple tension.

Hot Simple Bending Process Cold drawing Hot simple bending.

Rresent Inventive Proee ss Cold dravgingW- V I iot tension and bending. W

is cooled only to a certain temperature and passes around the rotary member in this unsatisfactory cooled state, thus causing permanent deformation, corresponding to the curvature of the rotary members, and reduced straightness.

Meanwhile, for the method for straightening wire for pre-stressed concrete construction, it has been proposed that steel wire which has been drawn at ambient temperature be subjected to continuous repeated bending at a temperature between 150 and 450C to straighten the wire thereby reduction of tensile Before describing the present inventive process, examples of apparatus for applying the present inventive process will be explained by referring to the attached drawings.

FIG. 1 and FIG. 2 show respectively a schematic side view of an example of the apparatus used for the present inventive process. FlG. 3 shows a schematic side view of the apparatus when the present inventive process is applied to the production of steel wire strand used for pre-stressed concrete construction. FIG. 4 is a schematic view for explaining the height of bending ble to stress relaxation but has excellent straightness are. FIG. 5 shows the effects on the relaxation value of the degree of bending and tension. FIG. 6 shows the effects on straightness of the degree of bending and tension. FIG. 7 compares the relaxation curves of the steel wire strand for pre-stressed concrete construction produced by the present invention and the steel wire strand produced by an ordinary process, from the same material.

The main construction of the apparatus for applying the present inventive process is composed of a tension machine (2 in FIG. 1, 2' in FIG. 2) for applying tension to the steel wire and wire strand, a heating device (4 in FIG. 1, 4a and 4'12 in FIG. 2 and 12 in FIG. 3) for heating steel wire 1, a straightener (5 in FIG. 1, 5 in FIG. 2 and 13 in FIG. 3), a cooling bath (6 in FIG. 1, 6 in FIG. 2 and 14 in FIG. 3), and a pulling capstan (7 in FIG. 1, 7' in FIG. 2 and 15 in FIG. 3).

The tension machine for applying tension to steel wire I to be treated may be of such structure as a simple brake drum since its required pulling force is small.

The heating of the steel wire 1 may be done by direct resistance heating, as shown in FIG. 1, or by pre- The cooling bath is important for improving the relaxation value and straightness of the processed steel wire as well as for the general feasibility of the process.

The pulling capstan must have a drum diameter more than 300 times that of the steel wire diameter in order to pull the tensioned steel wire and not to deteriorate its straightness.

In the apparatus shown in FIG. 1, the steel wire is heated mainly by an electric heating device. The steel wire supplied from the carrier is subjected to tension by tension device 2, and the thus tensioned steel wire 1 is heated to a predetermined temperature by direct resistance heating in heating device 4, which is composed of first heating electrode 3 and the second electrode which works also functions as straightener 5. The steel wire in the heated and tensioned condition is subjected to bending stress and straightened by straightener 5 (rollers for applying repeated bending or a rotary straightening machine, etc.). The hot worked steel wire is cooled in cooling bath 6 and pulled around capstan 7. In this arrangement, second electrode 5 is used as a straightener for the reason that the temperature of the heated steel wire is highest when the wire passes the second electrode and hence it is most effective to strighten the wire at this point.

In the embodiment of the apparatus shown in FIG. 2, the steel wire is pre-heated by gas furnace 4a and is uniformly heated by electric heating device 4b having electrode rollers 3'0 and 372 so as to obtain uniform heating with relatively small temperature gradient. Steel wire 1 is subjected to tension by tension device 2 and is uniformly heated by gas heating furnace 4a and electric heating device 4'b. Heated steel wire 1 is straightened by a straightener 5' (rollers for applying repeated bending or a rotary straightening machine etc.), then water-cooled in cooling bath 6 and taken up by capstan 7.

FIG. 3 shows an arrangement of apparatus used when the present invention is applied to the production of steel wire strand for pre-stressed concrete construction. Steel wire 9 is stranded into steel wire strand 10 by stranding machine 8 and the wire strand is wound once around winding drum 1]. Then steel wire strand 10 is heated by commonly used heating device 12 (induction heating furnace, tube type electric furnace. etc.), straightened by straightener 13 (rotary straightening machine, etc.), water-cooled in cooling bath l4 and taken up around capstan drum 15. The tension of the steel wire strand at this time is given by the working resistance and the speed variation between the winding machine and the capstan 15.

Next, the effect of the combination of tensile and bending stress applied by the present invention will be explained in comparison with the effect of other methods, and the recommended treating conditions of the present invention will be described. For the tension, the ratio of applied tension to actual ultimate tensile strength (hereinafter called specific load) is used. For the bending, a maximum strain (6 max) appearing on the wire surface can be used as the index. Thus, as shown in FIG. 4, in the case of the neutral line of a wire ofd diameter, the maximum strain can be expressed as below by the bend radius (R), the length of the chord of the bending are (l), and the height of the bending arc emax d/2/R emax 11/11 1 /4 d The height of the bending are necessary to give the maximum strain e max to the wire diameter d can be expressed as below In the case of steel wire strand, the height of the bending arc is given so as to produce the surface strain necessary for a single wire on the surface of outer component wires, with regard to the flexibility of the wire strand. The value can be obtained by multiplying.

Hereinafter, the bending condition will be expressed by the maximum strain for a single steel wire, while it will be expressed by the height of the bending arc and the length of the chord of the bending are for steel wire strand.

Embodiments of the present invention will be explained to clarify it. However, it should be understood the present invention is not limited to these embodiments.

Example I A single cold drawn steel wire having the composition (JIS SWRS 778), shown in Table 2, of5 mm diameter is subjected to the process of the present invention at a working temperature of 340C, with a maximum strain of 0.2 0.5 percent and a specific load 10 45 percent, to determine the effects on the relaxation and a straightness. FIG. 5 shows the variation in the relaxation value and FIG. 6 shows the variation in the straightness (expressed by the curvature of the wire).

Comparison is made with the results obtained by the simple working process in the same conditions.

chemical composition shown in FIG. 4, cold drawn and stranded, is subjected to the process of the present in- The relaxation test was performed at room temperature with 70% load of ultimate tensile strength.

It is clear from FIG. 5 that relaxation loss of 2.0 2.5

Table 2 C Si Mn P S Cu SWRS77B 0.78 0.24 0.77 0.014 0.012 0.02(%) Table 3 vention at a working temperature of 340C, with a height of bending arc of 6 mm, and a length of the Maxi- Specific Relaxation* Straight chord of the bending arc of 200 mm with various spemum n Strain q Loud c/r [M100 hr) CS5 clfic loads between 10 and 40 percent The effects 0 the relaxat1on value and phys1cal properttes are shown Ordinary in Table 5 in comparison with results obtained by the Process 0 O 30 ordinary process and the hot simple bending process. Hot Simple L6 bad Just as in Example 1, remarkable improvement of the Tension 0 143 relaxation is obtained by applying both bending and Process l .0 falr tension.

Table 4 C Si Mn P S Cu SWRS77B 0.75 0.24 0.77 0.019 0.013 0.01 72 Table 5 Relaxation 6B 602/68 Elongation (100 hr) kg/mm Ordinary Process 28 I94 89 5.0

Hot Simple Bending Process 2.4 195 92 6.0

Present Specific 10 L1 194 93 6.0 Invention Load (71) 20 0.9 195 93 6.5

Hot Simple Example 3 Bending 0.3 0 2.0 had Process 04 0 had 40 Steel wire strand of 6.3 mm diameter, having the 20 L0 good chemical composition shown in FIG. 6, cold drawn and P 03 8 e 3 stranded, is subjected to the process of the present inresent goo t O I mention 20 U good ventton at a worktng temperature of 370 C, wtth a spe- 0.4 30 0.9 good cific load of 40 percent and the length of the chord of 40 0.8 good the bending arc of 200 mm, with different heights of bending are 3 to 12 mm. The effects on the 1000 hr relaxation value and the straightness are shown in comparisonwith the results obtained by the hot simple tension process in Table 7. From the results it is apparent percent after 100 hours, with the hot simple bending that a height of bending arc of 3 to 9 mm is desirable.

process, is remarkably reduced when tension is applied, and this effect is considerable when compared with that obtained by the simple tensioning process. The same can be said of the effect on the straightness shown in FIG. 6. It is indicated that the effect is remarkable when the maximum strain is 0.2 to 0.5 percent, especially 0.3 to 0.4 percent, and the specific load is 10 to 45 percent, especially 25 to 45 percent.

Example 2 Steel wire strand of 9.3 mm diameter, having the Example 4 Table 8 Relaxation 88 50.2 Elonga- 92 (I000 hr) kg/mm kg/mm tion "/1 Ordinary Process 5.5 186 l67 6.0 Present Invention [.4 [86 177 6.0

As described above, a similar or lower relaxation value than that of the conventional processes can be obtained with less tension, as well as excellent straightness and similar or higher tensile strength, yield point and elongation are easily and stably obtained by the present invention, and thus it can be concluded the present invention is of considerable industrial value.

What is claimed is:

l. A method of producing steel wire and strand for prestressed concrete construction, having low relaxation value and excellent straightness, which comprises the steps of applying, in the ordinary low-temperature annealing range of 300 400C, to cold drawn steel wire and strand composed thereof, containing 0.6 0.9 percent of carbon, a tension corresponding to 10 7 50 percent of the tensile strength of the cold drawn wire at room temperature and, simultaneously applying a bending stress so as to give 0.1 0.5 percent maximum surface strain.

2. A method according to claim 1 in which the tension applied to the wire corresponds to 10 20 percent of the tensile strength of the wire at room temperature and in which bending stress is applied so as to give 0.4 0.5 percent maximum surface strain.

3. A method according to claim 1 in which the tension applied to the steel wire corresponds to 15 30 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.3 0.4 percent maximum surface strain.

4. A method according to claim 1 in which the tension applied to the steel wire corresponds to 25 45 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.25 0.45 percent maximum surface strain.

5. A method according to claim 1 in which the tension applied to the wire corresponds to 30 40 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.3 0.4 percent maximum surface strain.

6. A method according to claim 1 in which the tension applied to the wire corresponds to 35 45 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.2 0.3 percent maximum surface strain.

7. A method according to claim 1 in which the tension applied to the wire corresponds to 40 50 percent of the tensile strength of the wire, and in which bending stress is applied so as to give 0.1 0.2 percent maxi- 

1. A METHOD OF PRODUCING STEEL WIRE AND STRAND FOR PRESTRESSED CONCRETE CONSTRUCTION, HAVING LOW RELAXATION VALUE AND EXCELLENT STRAIGHTNESS, WHICH COMPRISES THE STEPS OF APPLYING, IN THE ORDINARY LOW-TEMPERATURE ANNEALING RANGE OF 300* - 400*C, TO COLD DRAWN STEEL WIRE AND STRAND COMPOSED THEREOF, CONTAINING 0.6 - 0.9 PERCENT OF CARBON, A TENSION CORRESPONDING TO 10 - 50 PERCENT OF THE TENSILE STRENGTH OF THE COLD DRAWN WIRE AT ROOM TEMPERATURE AND, SIMULTANEOUSLY APPLYING A BENDING STRESS SO AS TO GIVE 0.1 - 0.5 PERCENT MAXIMUM SURFACE STRAIN.
 2. A method according to claim 1 in which the tension applied to the wire corresponds to 10 - 20 pErcent of the tensile strength of the wire at room temperature and in which bending stress is applied so as to give 0.4 - 0.5 percent maximum surface strain.
 3. A method according to claim 1 in which the tension applied to the steel wire corresponds to 15 - 30 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.3 - 0.4 percent maximum surface strain.
 4. A method according to claim 1 in which the tension applied to the steel wire corresponds to 25 - 45 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.25 - 0.45 percent maximum surface strain.
 5. A method according to claim 1 in which the tension applied to the wire corresponds to 30 - 40 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.3 - 0.4 percent maximum surface strain.
 6. A method according to claim 1 in which the tension applied to the wire corresponds to 35 - 45 percent of the tensile strength of the wire and in which bending stress is applied so as to give 0.2 - 0.3 percent maximum surface strain.
 7. A method according to claim 1 in which the tension applied to the wire corresponds to 40 - 50 percent of the tensile strength of the wire, and in which bending stress is applied so as to give 0.1 - 0.2 percent maximum surface strain. 